The ThermoPlastic composites Research Center has successfully closed a two year collaborative project on the overmolding of thermoplastic composites with the design and manufacture of an advanced demonstrator part.

The part was realized as the result of a two year collaboration between TPRC, its members and renowned companies contributing from different areas of expertise: Autodesk, Harper Engineering Co., KraussMaffei, Safran S.A., Samvardhana Motherson Peguform (SMP) and Victrex PLC. The part features a typical grid stiffened panel that can be found in larger numbers in aerostructure applications. The stiffness and strength performance combined with extreme dimensional accuracy puts high demands on the manufacturing process.

Close-up of the Grid Stiffened Panel

The thermoplastic composite insert was press formed using TenCate Cetex® TC1225 engineered C/PAEK and subsequently overmolded with Victrex® PEEK90HMF40. The relatively low melting temperature of the composite material enables overmolding with PEEK at moderate insert temperature. The heat of the injected polymer is used to melt the surface of the solid insert upon contact. This makes the material combination extremely suitable for a two-step overmolding process.

Process design tools

The overmolding process combines the best of press forming and injection molding: A continuous fiber reinforced shell with relatively simple geometry was stiffened with a complex injection molded grid. However, tool design for injection molding is complex, and becomes even more challenging when the process is combined with continuous fiber reinforced thermoplastics. Numerical process design tools are indispensable for the composite engineer who more and more needs to take manufacturability into account in an early stage.

TPRC researchers Mark Bouwman, Thijs Donderwinkel and Jeroen Houwers worked on the experimental validation and modelling of the mechanisms underlying the overmolding process. They translated these to numerical models using a thermoforming software package (AniForm) combined with Autodesk Moldflow to predict interface strength and warpage caused by process-induced residual stresses.

Collaborative project

Franco Costa, Senior Research Leader at Autodesk Moldflow: “We have been very impressed with the quality of composites research at TPRC. The team at TPRC has demonstrated a great mix of practical process knowledge and a robust approach to modelling techniques and model development. The TPRC has also been very successful in bringing together into a collaborative project a broad range of companies which have each contributed from their own domain either equipment, materials expertise, process knowledge, modelling knowledge and software modelling. None of the partner company would have been able to achieve as much if they had been working alone – What has been achieved in collaboration is greater than the sum of the individual parts.”

Several TPRC partners will be displaying the demonstrators at the JEC WORLD 2017 from 14th of March until 16th of March. The JEC World tradeshow has the largest international gathering of composites professionals.

TPRC, the ThermoPlastic composites Research Center in the Netherlands, is an open innovation, research- and development center that aims for thermoplastic composites for a broad range of end use markets.